Electromagnetic horns



United States Patent 3,373,258 ELECTROMAGNETIC HORNS Maurice JamesAllport, Stourbridge, Engiand, assignor to Joseph Lucas (Industries)Limited, Birmingham, England, a British company Filed Feb. 15, 1967,Ser. No. 616,297 Claims priority, application Great Britain, Mar. 1,1966, 8,841/ 66 2 Ciaims. (Cl. 260-166) ABSTRACT OF THE DISCLOSURE Anelectromagnetic horn having means for compensating for wear of the fixedand movable contacts thereof.

This invention relates to electromagnetic horns of the kind comprising acasing, an electromagnet supported within the casing, an armaturereciprocable by the electromagnet and having a diaphragm connectedthereto, a fixed contact, a movable contact carried by a lever which isurged to a position in which the movable contact engages the fixedcontact, and a washer carried by the armature which can engage the freeend of said lever to move the movable contact out of engagement with thefixed contact to break the circuit to the electromagnet.

A known form of horn of this kind is shown in FIG- URE 1 of theaccompanying drawings, and the present invention will be more easilyunderstood after considering the construction of this known form ofelectromagnetic horn.

Referring to FIGURE 1, there is provided a cylindrical casing which atone end is formed with a neck 11, of reduced cross-section, the neck 11being closed at one end but formed with a central plunged hole so as todefine an axially extending integral sleeve 12. Located within the neck11, is an electromagnet 13, the pole piece 14 of which is in screwthreaded engagement with the sleeve 12.

The other end of the casing 10 is formed with an outwardly extendingperipheral flange 15 to which is secured a diaphragm 16 closing thecasing. Rigidly secured to the diaphragm 16 is the armature 17 of theelectromagnet 13, the armature extending axially within the casing 10 toa position spaced from the pole piece 14. The armature 17 is formed withan extension 18, which passes through the diaphragm, and to which issecured a tone plate 23.

When the electromagnet is energised, the armature 17 is drawn towardsthe pole piece 14 against the resilience of the diaphragm 16. As thearmature moves towards the pole piece 14, a fibre washer 21 engages alever 24, thereby opening a pair of contacts 22 in the casing, andbreaking the circuit to the electromagnet to allow the armature toreturn to its original position under the action of the daphragm 16. Thecontacts 22 then close and cycle is repeated so that the diaphragm isreciprocated to produce a sound.

The pole piece 14 is adjusted relative to the sleeve 12 to a positionsuch that the armature 17 strikes the pole piece 14 as the contacts 22are opened, so that the tone plate 23 produces a note which blends withthe note from the diaphragm to produce the sound of the horn. Afteradjustment, the pole piece is fixed in position, for example by Welding.

It is desirable in such horn constructions that the contact 22 shouldhave a large contact area and as shown 3,373,258. Patented Mar. 12, 1968in FIGURE 1 the contacts 22 have in the past been provided with flatmating surfaces. However a problem is encountered with suchconstructions in that it is dilficult to mount the contacts 22 in such amanner that the mating faces are accurately parallel. This problem isovercome by providing the contacts with domed faces which in use wear toprovide the required flat, parallel, mating surfaces. It is found,however, that as the contacts wear, the free end of the lever 24 movesto the left, as compared with FIGURE 1, when the contacts 22 are closed.Consequently the period of time during which the contacts are closeddecreases, resulting a corresponding change in the notes emitted by thehorn. The object of the present invention is to overcome thisditficulty.

According to the invention .a horn of the kind specified includes meansmovable with the free end of the lever and acting on the washer to causethe washer to wear so as to compensate for wear of the contacts.

In the accompanying drawings FIGURE 1 is a sectional view of the knownform of electromagnetic horn described above and FIGURE 2 is afragmentary sectional view of an electromagnetic horn similar to thatshown in FIGURE 1 but which embodies one example of the presentinvention.

Referring to the drawings it will be seen that the construction of thehorn in FIGURE 2 is very similar to that shown in FIGURE 1, componentscommon to both constructions being designated by the same referencenumerals. However, the contacts 22 in FIGURE 2 are domed and the lever24 is provided with an integral projection 25 which extends towards thefibre washer 21. The arrangement is such that in use the projection 25Wears a corresponding depression in the washer 21 at a ratesubstantially equal to the rate at which the contacts 22 wear, therebyensuring that the period of time in the cycle of operation during whichthe contacts 22 remain closed, is maintained substantially constant, andconsequently that the notes emitted by the horn are substantiallyconstant.

What is claimed is:

1. In an electromagnetic horn comprising a casing, .an electromagnetsupported within the casing, an armature reciprocable by theelectromagnet, a diaphragm connected to said armature, a fixed contactsupported by the casing, a lever supported by the casing and carryingintermediate its ends a movable contact, said lever having a free endadjacent said movable contact and said end being urged to a position inwhich said movable contact engages the fixed contact, and a washercarried by said armature, movement of said armature upon energisation ofsaid electromagnet moving said washer into engagement with the free endof said lever to move said movable contact out of engagement with saidfixed contact and so break the circuit to the electromagnet, theimprovement residing in providing said free end of the lever with a partwhich said washer engages, said part causing the washer to wear so as tocompensate for wear of said contacts.

2. An electromagnetic horn .as claimed in claim 1 in which said part isan integral projection formed on said lever.

References Cited FOREIGN PATENTS 1,222,394 8/1966 Germany.

ROBERT K. SCI-IAEFER, Primary Examiner. H. O. JONES, Assistant Examiner.

